We have recently defined a new HLA gene which maps centromeric to the other known genes of the HLA complex. Studies have now been initiated to study the distribution of SB antigens in two different disease populations in order to further understand the role of HLA genes in determining disease susceptibility--multiple sclerosis and dermatitis herpetiformis. In the 38 unrelated MS patients studied, there was no significant deviation in the frequency of SB antigens, relative to 200 normal control donors. However, among the 41 DH patients studied, there was a significant deviation from the normal donors, particularly with respect to an elevation of the frequency of the SB1 antigen and a decrease in the frequency of the SB2 antigen. These data cannot be explained by the known strong association between DH and DR3; rather they indicate that there is an interaction between the HLA-SB and the HLA-DR phenotype in determining the risk for dermatitis herpetiformis.